1. Field of the Invention
The present invention relates to a hard disk, a control unit for a disk device, and a method for controlling a disk device.
2. Description of the Related Art
In a disk device such as a magnetic disk device realizing the recording/reproducing operation by a head, the head seek is normally conducted by means of sector servo system so that the head can be disposed at a predetermined position of the disk. The head seek according to the sector servo system is conducted based on the servo data recorded in the disk (magnetic disk) as a recording medium. The servo data includes cylinder data (cylinder codes) representing cylinder numbers, sector data representing sector numbers (servo sector numbers) and burst data representing the position information (position errors in the cylinders represented by the corresponding cylinder data) as the corresponding amplitudes of waves.
The areas for the servo data to be recorded in the disk are called as “servo areas” which are arranged at a predetermined distance over the tracks in the disk so as to be elongated radially from the center thereof. The data areas (user areas) are provided between the servo areas, respectively, so that a plurality of data sectors are defined in each of the data areas. One servo area and the data area subsequent to the servo area constitute the servo sector.
In a magnetic disk device utilizing the position-determining control by means of the sector servo system, the writing operation may not be conducted when some scratches are formed at the surface of the magnetic disk. Conventionally, in this case, the user sector containing at least a portion of the data area with the scratches and functioning as an access unit from a host system is defined as a “disabled area”, so that an alternative sector provided in a corresponding spare area in the magnetic disk is allotted in substitution for the disabled user sector. In this case, a user continues to use the magnetic disk device even though the intended data area becomes disabled due to the scratches of the magnetic disk.
Reference 1 teaches that when the occurrence frequency of write fault is low, retry operation is conducted per user sector, and when the occurrence frequency is high, the corresponding servo sector is recognized as a disabled servo sector so that all of the data sectors to be conducted in write operation and containing the top data sector of write fault are substituted.
In Reference 1, however, the alternative process is conducted per user sector only if a servo sector is recognized as a disabled servo sector after the retry operation is conducted several times.
Recently, on the other hand, the length of user sector in a hard disk intends to be enlarged from 512 byte to 4 k byte so that the length of user sector may become larger than the length of serve sector, particularly in the inner area of the hard disk. In this case, the alternative operation per user sector may deteriorate the writing capacity for the hard disk.
In contrast, in Reference 1, since the alternative operation is conducted per user sector, the writing efficiency for the hard disk may be enhanced when the length of user sector becomes larger than the length of servo sector. In Reference 1, however, the alternative operation is conducted only if a given servo sector is recognized as a disabled servo sector after the repeated retry operation so that it takes a long period of time to conduct the alternative operation per servo sector.
[Reference 1] JP-A 10-275429 (KOKAI)